Tektronix 1S1 Instruction Manual page 26

Normally a zero triggering level is obtained with the
TRIGGER SENSITIVITY control set 45° clockwise from the
midrange (straight up) position. When the TRIGGER SOURCE
switch is set to the INT+ or EXT+ position, if the TRIGGER
SENSITIVITY control is turned clockwise from the zero level
position, the ac-coupled input triggering signal is moved in
the positive direction with respect to the fixed triggering level
of the circuit (see Fig. 2-9A and 2-9B). If the control is turned
counterclockwise, the triggering signal is moved in a negative
direction with respect to the triggering level (see Fig. 2-9C
and 2-91D). Trigger recognitions will be made in Fig. 2-9A
and 2-9C because the triggering signal passes through the
triggering level. In Fig. 2-9B, the trigger will free run, since
the input triggering signal is always more positive than the
triggering level. In Fig. 2-9D, the trigger will be held off,
since the triggering signal is always more negative than the
triggering level. The trigger circuit is most sensitive to small
signals when the TRIGGER SENSITIVITY control is set slightly
counterclockwise from the zero triggering level position.
If the TRIGGER SOURCE switch is set to the INT- or
EXT- position, the input triggering signal is inverted prior
Fig. 2-9. Operation of the TRIGGER SENSITIVITY control, with an input pulse amplitude of about 100mv external (or 1 volt
internal) and a repetition rate below 80 kc (see text).
Operating Instructions – Type 1S1
to being connected to the trigger circuit. In this case, nega-
tive-going pulse signals are changed to positive-going sig-
nals, then the triggering operation is the same as previously
described and trigger recognitions are made on negative-
going excursions of the input signal.
The TRIGGER SENSITIVITY control determines the input
triggering signal level that will cause the circuit to operate.
The amplitude and duty factor of the input signal will deter-
mine the effective range of the control operation (approxi-
mately 200mv when the signal is applied through the EXT
TRIG connector, and 2 volts when applied by way of the
SIGNAL IN connector). Normal triggering is accomplished
by setting the TRIGGER SENSITIVITY control so that the trig-
ger level coincides with the desired triggering level of the
input signal.
The repetition rate of the trigger circuit is established pri-
marily by the setting of the TIME POSITION RANGE switch
and is adjusted by means of the RECOVERY TIME control.
This holdoff period is designed to allow the fast ramp to
operate and reset properly between triggering events. Mini
2-17